There is a demand for apparatus capable of spraying chemicals in fluid form evenly and quickly over tracts of farmland and pasture land. The fluids may be used to control pests on or in the earth or on foliage into which crops are to be or have been sown, or to control the growth of plants such as standing crops or weeds.
Such fluids should be applied evenly and at an ascertained concentration if they are to be effective. This is particularly important with selective herbicides where too strong a concentration can adversely affect the crop or soil or required plant species. This imposes demands on the apparatus used to apply the chemicals.
A further problem is that the atmospheric conditions prevailing during spraying have to be taken into account. Ideally, the fluids are applied to the plants or ground in relatively low wind conditions. In practice, such conditions often occur at night and therefore such spraying can be carried out between dusk and dawn.
Ground spraying with liquid chemicals occurs at certain times of the year and is invariably entrusted to a contract sprayer who owns the appropriate equipment. At these times the services of a contract sprayer can be much in demand. Should he contract to spray on a day which is unsuitable, it may be some time before he again has adequate time available to undertake the spraying. For this reason it is desirable that when the conditions are right, spraying should be carried out as quickly as possible and in a way which is effective and does not risk damage to the crops or the soil in which they are sown.
Conventionally, liquid chemicals are applied to large tracts of land by a boom-spraying vehicle which may be power driven or in the form of a trailer. The vehicle has a tank containing the liquid which is pumped into a horizontally extending boom projecting away from one or both sides of the vehicle. The boom is provided with spaced apertures and/or metering devices directing sprays of liquid downwardly so that as the vehicle advances, the area directly beneath the boom is wetted with liquid at an even and constant rate. For convenience, the area directly beneath the boom which may be earth, vegetation or crops will hereafter be referred to as the "target area".
A number of factors in practice limit the speed at which liquid chemicals can be applied to land even when the atmospheric conditions are suitable for optimum results. Ideally the liquid should be applied at a preferred volume and pressure per unit target area and the vehicle should travel at a speed which enables this to be done as quickly as possible without loss of uniformity or accuracy in the application.
A pneumatically-tired vehicle can move faster over land than a tracked vehicle and, at least theoretically, can spray a larger area of land in a given time. However a pneumatically-tired vehicle is more susceptible to rocking when passing over rough or uneven ground than a tracked vehicle. Such rocking limits the length of boom that can Project from the side of the vehicle to about 20 feet. If the boom is longer, its end may dig into the ground when the vehicle rocks and be broken. Although a longer boom could be placed at a higher level on the vehicle, this greatly reduces the accuracy of application and reduces the penetration of the liquid onto the target area. In practice the maximum span of boom assembly is usually considered as being about 46 feet. The assembly has approximately a 6-foot long centre section extending across the width of the vehicle and two boom end-portions which project 20 feet from either side. Jointing is provided to enable the boom end-portions to be stowed, folded or removed when not in use.
A 46-foot boom mounted on a pneumatically-tired vehicle, is normally arranged at about 2 feet above ground level. However, uniform application and optimum spray penetration onto the target area is obtained when the boom is only 12-18 inches above the target area. Thus effectiveness of the spraying is sacrificed for speed. Other problems experienced with a 20-foot boom end-portion are that it tends to whip with vertical jolting movement of the vehicle thus reducing accuracy of application, and it may sag at its end and suffer fatigue cracking as a result of its weight.
The speed at which a pneumatically-tired boom spraying vehicle can operate satisfactorily is normally considered to be about 8-12 kilometers per hour. Bearing in mind that the width of the boom assembly is some 46 feet, such a vehicle can theoretically only spray up to about 170 hectares of land in 10 hours, if the land is even. If the land is rough or its topography is irregular, the speed of spraying has to be reduced and the time necessary to spray is correspondingly increased.
An object of the invention is to provide an improved boom spraying apparatus capable of operating at a higher degree of efficiency at a substantially higher speed than hitherto.